My long- term goal is to become a proficient independent clinical researcher addressing racial and ethnic differences in vitamin D and calcium nutrition. My career development plan includes a Master of Science in Clinical Research and mentored clinical and social research. I plan to study the vitamin D status of pre- and early adolescent African American and Caucasian children. Epidemiologic and clinical data document a high prevalence of vitamin D insufficiency among adults and adolescents in the US. Little is known about the prevalence, seasonal variation and the metabolic impact of vitamin D insufficiency in preadolescent children. In Phase 1, using a longitudinal study design, we will estimate the prevalence and seasonal variation of vitamin D insufficiency in children 6 to 12 years old and characterize its impact on bone metabolism. A cohort of 140 healthy pre- and early adolescent children (6-12 yrs old, Tanner I or II, African American [n=94] and Caucasian [n=46]) will be studied during summer (June through September) and winter (December through March). Vitamin D status, calcitrophic hormones and markers of bone turnover will be assessed during summer and winter. Other measures include dietary intakes of vitamin D and calcium, sun exposure and body mass index. This study will help establish the prevalence, seasonal variation, metabolic impact of vitamin D insufficiency in young school-age African American and Caucasian children. In phase 2,168 (African American: 84, Caucasian: 84) 8 to 14 year old preadolescent and adolescent children will undergo a randomized-placebo controlled trial (RCT) of vitamin D31000 ID daily vs. placebo for 6 months initiated during fall and winter (October through March). This study will determine the serum 25(OH)D cutoff for the definition of vitamin D insufficiency and document the safety and efficacy of treatment on vitamin D status. To address issues of health disparities we will use the study design to test the hypothesis that parental mistrust in medicine and research is a barrier to recruitment of African American children into clinical research compared to Caucasian children. Parents of children recruited for the vitamin D study will be surveyed. Differences in the trust index between consenting and declining groups of parents will be determined. The results should help develop strategies for overcoming those barriers. Prevention of vitamin D insufficiency in children will improve their bone health (increase the peak bone mass) and reduce their "osteoporosis burden" during adulthood. Optimizing vitamin D status in African American children may have the potential to reduce the disparities from non-skeletal disorders associated with chronic vitamin D insufficiency such as diabetes and prostate cancer that disproportionately affect African American adults.